Lecture 6

Question 1

how much has the human population increased in the last 200 years

Answer 1

Human population growth has increased 7-fold in the last 200 years

Question 2

Ramifications of exploitation of natural resources resulting in global problems

Answer 2

Disturbance to carbon, nitrogen and phosphorus cycles
Climate change, pollution
Deforestation

Question 3

Food Production per hectare may double by 2050

Answer 3

Still not enough ensure adequate food security for all

Question 4

What percentage of nitrogen and phosphorus isn’t absorbed by crops

Answer 4

~60% of nitrogen and 70-90% of phosphorus supplied to agricultural fields is not absorbed by the plants/ crops
Only 10 % of phosphorus applied to agricultural systems is consumed by humans (Rodríguez and Fraga, 1999; Richardson, 2001).

Question 5

Rock phosphate

Answer 5

In typical systems, only 30% of rock phosphate applied to an agricultural system is taken up by the plant

Question 6

Microbial innoculants

Answer 6

Bacteria/fungi
Enzymatic potential to release simple PO43- from various P forms (inorganic and organic)
Sold as commercial inoculants
Usually low efficacy in the field

Question 7

Problems with microbial inoculants

Answer 7

Rarely work in the field
Conditions are very different to lab conditions
Microorganisms are often limited for carbon in the soils
Rhizosphere less so but, not like laboratory conditions
Leads to a reduction in organic acids release
Good example is that organic acids released from plants are quickly degraded by rhizobacteria

Question 8

organic phosphates

Answer 8

Plants and microbes (bacterial and fungi) release alkaline and acid phosphatases (various mono/di-phosphoesterases), phytases (phytate), 5-nucleotidases (DNA), phosphodiesterases (phospholipids)
Leads to the release of simple PO4
Acid and alkaline phosphatases are thought to degrade hundreds of different compounds
Para-nitrophenol phosphate (PNPP), bromochloro inisitol phosphate (BCIP), 3-O-methylfluorescin phosphate
Poorly characterised
pH optimum - acids (pH 4-5), alkaline (pH 10)
PhoD, PhoX are the major phosphatases in soils

Question 9

low pH soils

Answer 9

Significant reduction of alkaline phosphates in low pH soils

Question 10

Brasica includes oil seed rape, the Uk;s 3rd most economically important corp

Answer 10

OSR does not have an assoication with mycrorrhizal fungi , the bacteria in the rhizosphere are important in supplying phosphorus to the plant